1. Field of the Invention
The present invention relates to a wireless communication device which is adapted for use in a bidirectional wireless system and, more particularly, to a wireless communication device and a signal processing unit which are able to enhance sensitivity in a correlation peak detection processing.
2. Description of the Related Art
[Bidirectional Wireless System: FIG. 12]
A wireless communication device that has been conventionally used in a bidirectional wireless system adopts a spread spectrum scheme to operate in weak radio waves.
The conventional bidirectional wireless system will be described with reference to FIG. 12. FIG. 12 is a schematic diagram illustrating the conventional bidirectional wireless system.
The conventional bidirectional wireless system is provided with a wireless communication device as a master device 1 which has a transmitting unit 1a and a receiving unit 1b, and a wireless communication device as a slave device 2 which has a transmitting unit 2a and a receiving unit 2b. The conventional bidirectional wireless system transmits operation commands from the slave device 2 to the master device 1 by operating an input device of the slave device 2, so that the master device 1 is operated according to the commands.
The master device 1 is to transmit responses to transmission states of the commands or state information of the master device 1 to the slave device 2.
That is, the conventional bidirectional wireless system is a weak wireless system capable of performing bidirectional communication (half duplex) adopting the SS.
In the bidirectional wireless system, the slave device 2 plays a leading role in operation. The master device 1 receives the commands from the slave device 2 by intermittently receiving the transmission from the slave device 2, and the slave device 2 is put into an operation mode only when it is to be operated. Therefore, it is possible to significantly reduced power consumption.
[Configuration of Conventional Signal Processing Unit: FIG. 13]
A signal processing unit in the wireless communication device will be described with reference to FIG. 13. FIG. 13 is a block diagram illustrating a configuration of a conventional signal processing unit.
The conventional signal processing unit is provided with an ADC (Analog Digital Converter) control unit 11, an AGC (Auto Gain Control) unit 12, APC/AFC (Auto Power Control/Auto Frequency Control) control unit 13, a DAC (Digital Analog Converter) control unit 14, a carrier demodulating unit 15, a carrier data generating unit 16, a carrier modulating unit 17, a receiving data decoding unit 18′, a spread code generating unit 20′, a spread modulating unit 21′, a correlation peak detecting unit 22′, a coarse frequency deviation detecting unit 23′, and a fine frequency deviation detecting unit 24′.
Parts of the conventional signal processing unit will now be described in detail.
The ADC control unit 11 performs control to generate a control signal for the A/D converter (designated as “A/D”), and to receive a receiving IF (Intermediate Frequency) signal as an input signal from the A/D converter.
The AGC unit 12 controls a gain control signal which is outputted to the AGC amplifier in a wireless communication unit, so that the receiving IF signal output coming from the ADC control unit 11 may always be kept to have a predetermined amplitude.
The APC/AFC control unit 13 receives, as an input thereto, the control signal for monitoring temperature of the wireless communication unit from the A/D converter using a thermistor, and outputs an AFC correction value and an APC correction value to the carrier data generating unit 16 and the carrier modulating unit 17, respectively, with respect to the monitored value.
The DAC control unit 14 delivers data, which is modulated in carrier by the carrier modulating unit 17, to the D/A converter.
The carrier demodulating unit 15 performs a processing of removal of an IF carrier component with respect to the receiving IF signal which is outputted from the ADC control unit 11 and further a down sample processing on the afore-processed signal, and then outputs the eventual signal to the receiving data decoding unit 18′, the correlation peak detecting unit 22′, and the coarse frequency deviation detecting unit 23′, respectively.
The carrier data generating unit 16 performs a frequency correction processing according to a frequency deviation value or the like from the coarse frequency deviation detecting unit 23′ and the fine frequency deviation detecting unit 24′, and generates IF carrier data to be supplied to the carrier demodulating unit 15 and the carrier modulating unit 17.
The carrier modulating unit 17 performs an APC correction processing according to an APC correction request from the APC/AFC control unit 13, with respect to the IF carrier data which is supplied from the carrier data generating unit 16, and also performs the carrier modulation processing with the IF carrier data, with respect to spread modulation processing data which is input from the spread modulating unit 21′.
The receiving data decoding unit 18′ detects a synchronizing word after performing a fine frequency correction of a synchronized IF carrier frequency, and performs a demodulation processing of user data.
The spread code generating unit 20′ generates a spread code which is used in performance of a spread modulation and a reverse spread processing. At this stage, two types of spread codes are necessary to be used for synchronizing word/REF (Reference) data and for the user data.
The spread modulating unit 21′ performs a differentially-encoding processing of the synchronizing word/REF data and the spread modulation processing of the transmission user data and the synchronizing word/REF data after being differentially encoded.
The correlation peak detecting unit 22′ performs a correlation processing on a carrier demodulated data which is outputted from the carrier demodulating unit 15 to perform a correlation peak detection.
The coarse frequency deviation detecting unit 23′ detects residual frequency components according to an IF carrier frequency deviation amount between the master device and the slave device on the carrier demodulated data which is outputted from the carrier demodulating unit 15, and outputs the frequency deviation amount to the carrier data generating unit 16.
The fine frequency deviation detecting unit 24′ performs frequency detection at a high accuracy on the correlation data of which a peak has been detected, in order to further decrease the frequency deviation amount, and outputs the fine frequency deviation amount to the carrier data generating unit 16.
Further, in the correlation peak detecting processing of the signal processing unit of the conventional wireless communication device, the peak detection is carried out by comparing a fixed threshold value or a complicatedly processed variable threshold value with respect to the detected correlation value.
[Prior Art]
Further, there are Japanese Patent Application Laid-Open No. 2000-115027 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2002-290272 (Patent Document 2) as related prior arts.
Patent Document 1 discloses a spread spectrum communication method and a device thereof. In Patent Document 1, a correlation output is detected over a data region by a peak detector, and the detected data becomes a correlation peak. When the correlation peak value exceeds a threshold value of a comparator, a peak value and a peak position of the correlation peak are secured. Then, when the correlation peak value is larger than the threshold value in an observation region which is narrower than the data region and when detected over a predetermined number of times, the synchronization is established.
Patent Document 2 discloses a path detection device which detects a timing position of a path where a correlation waveform is maximized. In Patent Document 2, when a current synthesized over one period of a spread spectrum code is larger than the maximum value of a previous synthesized current in a period of time for counting clock pulses, memory is updated and the counted value is outputted.
However, in the correlation peak detecting processing of the signal processing unit of the conventional wireless communication device, since the peak detection is carried out by comparing the fixed threshold value or the complicatedly processed variable threshold value with respect to the detected correlation value, it is impossible to obtain a threshold value up to the limit with respect to a variation of the peak value generated under a weak electric field environment or from individual differences between devices in any case, so that a probability of false detection is increased. When a margin is designed to a certain extent, this leads to a problem that the sensitivity of detection is significantly degraded.